1. Field of the Invention
This invention relates to a tire air valve having a function of indicating tire pressure, particularly to the one whose cap at upper end of the tire air valve can be determined whether the condition of tire pressure is normal or not by visual sight, able to insure safety of driving a car.
2. Description of the Prior Art
Generally, for the sake of safety, before starting a journey, an automobile ought to be inspected in many aspects, inclusive of the volume of gasoline, the condition of water tank, the brake system, the lights, tire pressure and so on. In order to keep the tire pressure in a normal condition is extremely important to insure safety of driving a car, however, most drivers inspect the tire pressure of all tires in a way of visual observation, that is, whether the tire pressure is sufficient or not is judged by visual sight about the extent of deformation of a tire. In fact, the way of visual observation is not possible to precisely judge whether the tire pressure is normal or inflating the tire is needed forthwith. Therefore, accurate inspection of tire pressure is necessary to be carried out in an automobile maintenance and repair shop or by providing a tire pressure detector, thus resulting in much inconvenience. In view of such a situation, various kinds of electronic tire pressure indicating apparatus have come into existence; nevertheless, such electronic tire pressure indicating apparatus are complicated in structure, high price, difficult assembly, and also easy to cause short circuit to disable operating of the apparatus normally and losing a warning function of tire pressure. Another conventional tire pressure as “AIR VALVE CAP HAVING FUNCTION OF INDICATING TIRE PRESSURE” is directly assembled on the upper side of a tire air valve to be pushed by the pressure in a tire. This conventional tire pressure indicating apparatus is composed of a main base, a thimble, a transparent section and an indicating member. A cap is locked on a tire air valve so that the pressure in a tire can be directly transmitted into the cap to push the indicating member, which matches with a transparent tube of the air valve cap and is divided into a red-colored region and a green-colored region. When the indicating member is located in the green-colored region, it means that the tire pressure is normal, and when the indicating member lies in the red-colored region, it means that the tire pressure is deficient, thus letting the cap serve as a detector and an indicator of tire pressure. However, if the cap of this conventional air valve, which is installed on the air valve and has function of indicating tire pressure, gets cracks or becomes damaged by bumping, air in the tire will leak out through the cracked portion from the cap and as a consequence, dangers may occur during driving in case the driver does not find the rupture of the cap and replace it with a new one on time.